Raman effect

the change in wavelength of light scattered while passing through a transparent medium, the collection of new wavelengths (Raman spectrum) being characteristic of the scattering medium and differing from the fluorescent spectrum in being much less intense and in being unrelated to an absorption band of the medium.

Raman effectThe alteration of the frequency and the phase of light as it passes through a transparent medium. The Raman effect is caused by small differences between the energy of photons absorbed by the molecules that make up the medium and the energy of photons re-emitted.